1. Field of the Invention
The present invention relates to a fundus photographing device to be used in ophthalmology clinics, and particularly to a fundus photographing device for fluorescent photography with infrared light.
2. Description of Related Art
There has been known a fundus photographing device for photographing an image of a fundus with infrared fluorescence emitted from choroidal veins of an examinee""s eye. For the photography, indocyanine green (hereinafter referred to as ICG) which is a fluorescent agent is intravenously injected at first into the choroidal veins. The fundus of the examinee""s eye is then illuminated with infrared light to excite the ICG circulated in the fundus (the choroidal veins). Thus the image of the fundus is photographed by the fundus photographing device with the infrared fluorescence emitted from the choroidal veins.
ICG has a peak absorption wavelength in a range of about 780 nm to 805 nm. In the infrared fluorescence photography using ICG, generally, the fundus is illuminated with exciting light through an exciter filter capable of sufficiently transmitting light of wavelengths of above 780 nm, while cutting light of wavelengths of about 800 nm or more. On the other hand, the ICG circulated in the fundus (the choroidal veins) and excited by the exciting light will emit fluorescence with a peak of about 830 nm. To prevent false fluorescence resulting from the exciting light from being mixed in a fluorescence photograph, the photography is carried out through a barrier filter capable of filtering fluorescence to allow transmission of the fluorescence having long wavelengths of about 820 nm or more.
Instead of the device using the exciter filter, there has recently been proposed a photographing device using, as an exciting light source, a laser diode which is a light source that emits light of a single wavelength having a peak of about 790 nm.
However, the infrared fluorescence of ICG emitted from the fundus (the choroidal veins) is very faint, which is about {fraction (1/25)} to {fraction (1/50)} in fluorescent intensity as compared with the fluorescence in a visible fluorescence photography using fluorescein as a fluorescent agent. Thus, the conventional device could only photograph the eye fundus with fluorescence of very low luminance. Therefore, thee are tendencies that only the sites where blood vessels lie on top of one another or plural blood vessels gather can be observed. In particular, the fluorescence at the early stage of ICG injection into the choroidal veins could hardly be captured. As a result, there were many insufficiencies in observation and photography of the choroidal circulation dynamics.
The present invention has been made in view of the above circumstances and has an object to overcome the above problems and to provide a fundus photographing device capable of efficiently photographing the fundus of an examinee""s eye with infrared fluorescence of high luminance, thereby providing more detailed information for diagnosis of choroidal circulation dynamics of the examinee""s eye.
Additional objects and advantages of the invention will be set forth in part in the description which follows and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the purpose of the invention, there is provided a fundus photographing device for conducting infrared fluorescence photography on a fundus of an examinee""s eye after intravenously injecting a fluorescent agent which emits fluorescence of an infrared region into veins, the device including: an illumination optical system for illuminating the fundus with exciting light, thereby exciting the injected fluorescent agent, the exciting light being of wavelengths in a wavelength region of not maximum absorption but maximum fluorescent intensity of the fluorescent agent.
According to another aspect of the present invention, there is provided a fundus photographing device for conducting infrared fluorescence photography on a fundus of an examinee""s eye after intravenously injecting a fluorescent agent which emits fluorescence of an infrared region into veins, the device including: an illumination optical system for illuminating the fundus with exciting light, thereby exciting the injected fluorescent agent, the exciting light being of wavelengths with a peak in a range of approximately 725 nm to 745 nm; and a photographing optical system including filtering means for filtering infrared fluorescence from the injected fluorescent agent and a photographing element for photographing an image of the fundus with the infrared fluorescence filtered through the filtering means.
Moreover, according to another aspect of the present invention, there is provided a fundus photographing device for conducting infrared fluorescence photography on a fundus of an examinee""s eye after intravenously injecting a fluorescent agent which emits fluorescence of an infrared region into veins, the device including: an illumination optical system for illuminating the fundus with exciting light of wavelengths in a predetermined wavelength region, thereby exciting the injected fluorescent agent; and a photographing optical system including a barrier filter for filtering infrared fluorescence from the injected fluorescent agent and a photographing element for photographing an image of the fundus with the infrared fluorescence filtered through the barrier filter, the barrier filter having a property of transmitting wavelengths in a predetermined wavelength region different from the wavelength region of the exciting light.